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          CSS+HTML系列
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  CSS的BFC
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          JS系列
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  JS-原型与原型链
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  JS-执行上下文
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          Vue2系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/web/vue/mvvm.html" class="nav-link">
  Vue响应式
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          常见面试题
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  CSS面试题
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  Vue2.x面试题
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="Java" class="dropdown-title"><span class="title">Java</span> <span class="arrow down"></span></button> <button type="button" aria-label="Java" class="mobile-dropdown-title"><span class="title">Java</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          基础系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/basics/know.html" class="nav-link">
  Java初识
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  Java数字
</a></li><li class="dropdown-subitem"><a href="/java/basics/string.html" class="nav-link">
  Java字符串
</a></li></ul></li><li class="dropdown-item"><h4>
          集合
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/collection/collection.html" class="nav-link">
  Collection集合
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  List集合
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          IO操作
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/io/" class="nav-link">
  IO初识
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          网络编程
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  IP操作
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          JDBC操作
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/jdbc/mysql-connect.html" class="nav-link">
  MySQL操作
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          MySQL系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/database/mysql/init.html" class="nav-link">
  常用语法
</a></li><li class="dropdown-subitem"><a href="/database/mysql/data-type.html" class="nav-link">
  数据类型
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="设计模式" class="dropdown-title"><span class="title">设计模式</span> <span class="arrow down"></span></button> <button type="button" aria-label="设计模式" class="mobile-dropdown-title"><span class="title">设计模式</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/designMode/observer.html" class="nav-link">
  观察者模式
</a></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="运维/工具" class="dropdown-title"><span class="title">运维/工具</span> <span class="arrow down"></span></button> <button type="button" aria-label="运维/工具" class="mobile-dropdown-title"><span class="title">运维/工具</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          Maven
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  初识
</a></li></ul></li><li class="dropdown-item"><h4>
          Tomcat
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/tools/tomcat/" class="nav-link">
  初识
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="English" class="dropdown-title"><span class="title">English</span> <span class="arrow down"></span></button> <button type="button" aria-label="English" class="mobile-dropdown-title"><span class="title">English</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          英语读音
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/english/pronunciation/phonogram.html" class="nav-link">
  音标
</a></li></ul></li><li class="dropdown-item"><h4>
          英语单词
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/english/word/call.html" class="nav-link">
  电话
</a></li><li class="dropdown-subitem"><a href="/english/word/daily-life.html" class="nav-link">
  日常生活
</a></li><li class="dropdown-subitem"><a href="/english/word/animal.html" class="nav-link">
  动物
</a></li></ul></li><li class="dropdown-item"><h4>
          英语语法
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/english/grammar/sentence.html" class="nav-link">
  句子成分
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="Study" class="dropdown-title"><span class="title">Study</span> <span class="arrow down"></span></button> <button type="button" aria-label="Study" class="mobile-dropdown-title"><span class="title">Study</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/study/computers/" class="nav-link">
  计算机基础
</a></li><li class="dropdown-item"><!----> <a href="/study/web/" class="nav-link">
  前端知识路线
</a></li><li class="dropdown-item"><!----> <a href="/study/java/" class="nav-link">
  Java知识路线
</a></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="Self" class="dropdown-title"><span class="title">Self</span> <span class="arrow down"></span></button> <button type="button" aria-label="Self" class="mobile-dropdown-title"><span class="title">Self</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/self/work/" class="nav-link">
  工作
</a></li></ul></div> <!----></div> <!----></nav> <div class="loginItem"><!----></div></div></header> <div class="sidebar-mask"></div> <aside class="sidebar"><nav class="nav-links"><div class="nav-item"><!----> <a href="/" class="nav-link">
  首页
</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="导航" class="dropdown-title"><span class="title">导航</span> <span class="arrow down"></span></button> <button type="button" aria-label="导航" class="mobile-dropdown-title"><span class="title">导航</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/nav/nav.html" class="nav-link">
  常用站点
</a></li><li class="dropdown-item"><!----> <a href="/nav/web.html" class="nav-link">
  前端站点
</a></li><li class="dropdown-item"><!----> <a href="/nav/afterEnd.html" class="nav-link">
  后端站点
</a></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端" class="dropdown-title"><span class="title">前端</span> <span class="arrow down"></span></button> <button type="button" aria-label="前端" class="mobile-dropdown-title"><span class="title">前端</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          CSS+HTML系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/web/csshtml/css-formatContent.html" class="nav-link">
  CSS格式化上下文
</a></li><li class="dropdown-subitem"><a href="/web/csshtml/css-bfc.html" class="nav-link">
  CSS的BFC
</a></li></ul></li><li class="dropdown-item"><h4>
          JS系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/web/js/js-prototype.html" class="nav-link">
  JS-原型与原型链
</a></li><li class="dropdown-subitem"><a href="/web/js/js-context.html" aria-current="page" class="nav-link router-link-exact-active router-link-active">
  JS-执行上下文
</a></li></ul></li><li class="dropdown-item"><h4>
          Vue2系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/web/vue/mvvm.html" class="nav-link">
  Vue响应式
</a></li></ul></li><li class="dropdown-item"><h4>
          常见面试题
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/web/question/css.html" class="nav-link">
  CSS面试题
</a></li><li class="dropdown-subitem"><a href="/web/question/vue.html" class="nav-link">
  Vue2.x面试题
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="Java" class="dropdown-title"><span class="title">Java</span> <span class="arrow down"></span></button> <button type="button" aria-label="Java" class="mobile-dropdown-title"><span class="title">Java</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          基础系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/basics/know.html" class="nav-link">
  Java初识
</a></li><li class="dropdown-subitem"><a href="/java/basics/number.html" class="nav-link">
  Java数字
</a></li><li class="dropdown-subitem"><a href="/java/basics/string.html" class="nav-link">
  Java字符串
</a></li></ul></li><li class="dropdown-item"><h4>
          集合
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/collection/collection.html" class="nav-link">
  Collection集合
</a></li><li class="dropdown-subitem"><a href="/java/collection/list.html" class="nav-link">
  List集合
</a></li></ul></li><li class="dropdown-item"><h4>
          IO操作
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/io/" class="nav-link">
  IO初识
</a></li></ul></li><li class="dropdown-item"><h4>
          网络编程
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/network/ip.html" class="nav-link">
  IP操作
</a></li></ul></li><li class="dropdown-item"><h4>
          JDBC操作
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/java/jdbc/mysql-connect.html" class="nav-link">
  MySQL操作
</a></li></ul></li></ul></div> <!----></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="数据库" class="dropdown-title"><span class="title">数据库</span> <span class="arrow down"></span></button> <button type="button" aria-label="数据库" class="mobile-dropdown-title"><span class="title">数据库</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>
          MySQL系列
        </h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/database/mysql/init.html" class="nav-link">
  常用语法
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  数据类型
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  工作
</a></li></ul></div> <!----></div> <!----></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>CSS+HTML系列</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>JS系列</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/web/js/js-bom.html" class="sidebar-link">JS-BOM操作</a></li><li><a href="/web/js/js-dom.html" class="sidebar-link">JS-DOM操作</a></li><li><a href="/web/js/js-event.html" class="sidebar-link">JS-事件</a></li><li><a href="/web/js/js-function.html" class="sidebar-link">JS-函数</a></li><li><a href="/web/js/js-prototype.html" class="sidebar-link">JS-原型与原型链</a></li><li><a href="/web/js/js-context.html" aria-current="page" class="active sidebar-link">JS-执行上下文</a></li><li><a href="/web/js/js-variable.html" class="sidebar-link">JS-变量对象</a></li><li><a href="/web/js/js-scope-chain.html" class="sidebar-link">JS-作用域和作用域链</a></li><li><a href="/web/js/js-this1.html" class="sidebar-link">JS-This（一）</a></li><li><a href="/web/js/js-this2.html" class="sidebar-link">JS-This (二)</a></li><li><a href="/web/js/js-closure.html" class="sidebar-link">JS-闭包</a></li><li><a href="/web/js/js-data-type.html" class="sidebar-link">JS-基础类型和引用类型</a></li><li><a href="/web/js/js-new.html" class="sidebar-link">JS-new操作符</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue2.x系列</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3.x系列</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>常见面试题</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="main"><div class="content"><div class="theme-default-content content__default"><h1 id="js-执行上下文"><a href="#js-执行上下文" class="header-anchor">#</a> JS-执行上下文</h1> <p></p><div class="table-of-contents"><ul><li><a href="#生命周期">生命周期</a><ul><li><a href="#创建阶段">创建阶段</a></li><li><a href="#执行阶段">执行阶段</a></li></ul></li><li><a href="#可执行代码类型">可执行代码类型</a></li><li><a href="#执行上下文栈">执行上下文栈</a><ul><li><a href="#全局执行代码">全局执行代码</a></li><li><a href="#函数执行代码">函数执行代码</a></li></ul></li><li><a href="#执行上下文中三个对象">执行上下文中三个对象</a></li></ul></div><p></p> <p>🐴</p> <h2 id="生命周期"><a href="#生命周期" class="header-anchor">#</a> 生命周期</h2> <p>在<code>ECMAScript</code> 中当进入可执行代码（executable code）时，会进入一个叫做执行上下文（Execution context ）的环境。在该环境中为代码的执行做了一些前期准备。执行上下文主要分为<code>创建阶段</code> 和 <code>执行阶段</code> 两个阶段</p> <h3 id="创建阶段"><a href="#创建阶段" class="header-anchor">#</a> 创建阶段</h3> <p>在创建阶段主要做了</p> <ul><li>生成变量对象 （创建<code>arguments</code>, 检索函数声明，检索变量声明）</li> <li>建立作用域链</li> <li>确定<code>this</code>的指向</li></ul> <h3 id="执行阶段"><a href="#执行阶段" class="header-anchor">#</a> 执行阶段</h3> <p>在执行阶段主要做了</p> <ul><li>变量赋值</li> <li>函数的引用</li> <li>执行其它代码</li></ul> <div class="imageWrapper" data-v-a88366f6><div class="image" data-v-a88366f6><img src="img/web/js/context1.jpg" alt width="700" data-v-a88366f6></div> <!----> <div class="imgModel" style="display:none;" data-v-a88366f6><img src="img/web/js/context1.jpg" class="scaleImg" data-v-a88366f6></div></div> <h2 id="可执行代码类型"><a href="#可执行代码类型" class="header-anchor">#</a> 可执行代码类型</h2> <p>在<code>javascript</code>中可执行代码有三种：</p> <ul><li><code>全局代码</code></li> <li><code>函数代码</code></li> <li><code>evel</code>代码</li></ul> <p>当js引擎遇到这些代码时，就会创建一个执行上下文，并为这些代码的执行做一些前期的准备工作，比如 变量提升，函数提升，<code>this</code>确定等等，这些我们会在后面的文章中去介绍。</p> <h2 id="执行上下文栈"><a href="#执行上下文栈" class="header-anchor">#</a> 执行上下文栈</h2> <p>在<code>javascript</code>可执行的代码会有很多，那么所产生的执行上下文相应的也会有很多，而<code>js</code>是则会通过<code>执行上下文栈（Execution context stack）</code> 来管理这些<code>执行上下文</code>。</p> <h3 id="全局执行代码"><a href="#全局执行代码" class="header-anchor">#</a> 全局执行代码</h3> <p>我们可以将执行上下文栈当做一个数组来看，并且全局代码中的执行上下文永远会在执行上下文栈的最底部：</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// 伪代码</span>

ECStack <span class="token operator">=</span> <span class="token punctuation">[</span> <span class="token comment">// 执行上下文栈</span>
   globalContext  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>
</code></pre></div><h3 id="函数执行代码"><a href="#函数执行代码" class="header-anchor">#</a> 函数执行代码</h3> <p>当<code>javascript</code>遇到函数执行的代码时，也会创建一个执行上下文并推入执行上下文的堆栈中, 并将当前指针执行推入的执行上下文</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">&quot;执行&quot;</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token boolean">false</span>
<span class="token punctuation">}</span>
<span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 执行时才会创建执行上下文</span>

<span class="token comment">// 伪代码</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> functionContext<span class="token punctuation">)</span>

<span class="token comment">// ECStack 将变成下面这样</span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span> 
   <span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> functionContext<span class="token punctuation">,</span> <span class="token operator">&lt;</span><span class="token operator">--</span> pointer
   globalContext<span class="token punctuation">,</span>  
<span class="token punctuation">]</span>
</code></pre></div><p>上面例子当函数<code>fun</code>内部遇到 <code>return</code> 或执行结束后, 执行上下文栈中将会清楚<code>fun</code>函数的执行上下文，并将指针指向下面的执行上下文<code>globalContext</code></p> <p>我们在来看下面这个例子</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// 案例一</span>
<span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
<span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token comment">// 案例二</span>
<span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> f
<span class="token punctuation">}</span>
<span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token comment">// 案例三</span>
<span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> f
<span class="token punctuation">}</span>
<span class="token keyword">var</span> newFun <span class="token operator">=</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token function">newFun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
</code></pre></div><p>我们现在来分析一下这几个例子中执行上下文是如何放入执行上下问栈中的。</p> <p><strong>案例一：</strong></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
<span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token comment">// 伪代码</span>

<span class="token comment">// 进入全局代码环境时</span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
   globalContext  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>
<span class="token comment">// fun 函数执行时</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 在fun函数中的f() 执行时</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     <span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContex<span class="token punctuation">,</span>  <span class="token comment">// f执行上下文</span>
     <span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">,</span> <span class="token comment">// fun执行上下文</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

<span class="token comment">// 函数f执行完成后</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContext<span class="token punctuation">)</span>

<span class="token comment">// 函数fun执行完成后</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

当全局代码执行完成后，执行上下文栈中将是空的。
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
</code></pre></div><p><strong>案例二：</strong></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> f
<span class="token punctuation">}</span>
<span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token comment">// 伪代码</span>

<span class="token comment">// 进入全局代码环境时</span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
   globalContext  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>
<span class="token comment">// fun 函数执行时</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 因为函数f在fun函数中并没有执行，而是返回了，fun执行结束了</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

<span class="token comment">// fun函数执行完成后返回了函数f并执行函数f</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     <span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContext<span class="token punctuation">,</span>  <span class="token comment">// f执行上下文</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

<span class="token comment">// 函数f执行完成后</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>f<span class="token operator">&gt;</span> fContext<span class="token punctuation">)</span>

当全局代码执行完成后，执行上下文栈中将是空的。
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
</code></pre></div><p><strong>案例三：</strong></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">function</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">return</span> f
<span class="token punctuation">}</span>
<span class="token keyword">var</span> newFun <span class="token operator">=</span> <span class="token function">fun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token function">newFun</span><span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token comment">// 伪代码</span>

<span class="token comment">// 进入全局代码环境时</span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
   globalContext  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>
<span class="token comment">// fun 函数执行时</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 因为函数f在fun函数中并没有执行，而是返回了，fun执行结束了</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>fun<span class="token operator">&gt;</span> funContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

<span class="token comment">// fun函数执行完成后返回了函数f并赋值给了newFun函数</span>
ECStack<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>newFun<span class="token operator">&gt;</span> newFunContext<span class="token punctuation">)</span>

<span class="token comment">// 此时ECStack </span>
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span>
     <span class="token operator">&lt;</span>newFun<span class="token operator">&gt;</span> newFunContext<span class="token punctuation">,</span>  <span class="token comment">// f执行上下文</span>
     globalContext<span class="token punctuation">,</span>  <span class="token comment">// 全局执行上下文</span>
<span class="token punctuation">]</span>

<span class="token comment">// 函数newFun执行完成后</span>
ECStack<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token operator">&lt;</span>newFun<span class="token operator">&gt;</span> newFunContext<span class="token punctuation">)</span>

当全局代码执行完成后，执行上下文栈中将是空的。
ECStack <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
</code></pre></div><h2 id="执行上下文中三个对象"><a href="#执行上下文中三个对象" class="header-anchor">#</a> 执行上下文中三个对象</h2> <p>上面我们说了在JavaScript执行一段可执行的代码时会创建一个执行上下文，为代码的执行做一些前期准备。这个执行上下文具有三个很重要的对象：</p> <ul><li><a href="/web/js/js-variable">变量对象(Variable object，VO)</a></li> <li><a href="/web/js/js-scope-chain">作用域链(Scope chain)</a></li> <li><a href="/web/js/js-this1">this 对象</a></li></ul> <p>关于这三个对象在接下来的文章中我们去详细的讨论。</p> <hr> <p><strong>参考文章</strong></p> <ul><li><a href="https://developer.mozilla.org/zh-CN/docs/Web/API/HTML_DOM_API/Microtask_guide/In_depth#javascript_%E6%89%A7%E8%A1%8C%E4%B8%8A%E4%B8%8B%E6%96%87" target="_blank" rel="noopener noreferrer">JavaScript 执行上下文<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="http://www.cnblogs.com/TomXu/archive/2012/01/13/2308101.html" target="_blank" rel="noopener noreferrer">执行上下文<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://zhuanlan.zhihu.com/p/72959191" target="_blank" rel="noopener noreferrer">理解JavaScript的执行上下文<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://www.jianshu.com/p/6f8556b10379" target="_blank" rel="noopener noreferrer">JS 执行上下文<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">最近更新时间:</span> <span class="time">7/2/2021, 11:27:27 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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